Catalytic combustion can be used to provide efficient combustion at relatively low temperatures. The use of a combustion catalyst can achieve near complete combustion of a fuel/air mixture, thus avoiding the emission of high amounts of nitric oxides, carbon monoxide and unreacted fuel(s). Moreover, because the percentage of fuel in the mixture can be quite low, the mixture may not be flammable at atmospheric pressure in the absence of a catalyst. Catalytic combustors can also be relatively compact in size, reliable and quiet in operation.
Catalytic combustors are known for use in various mobile applications. In addition, such combustors can be integrated with gas turbines for partially oxidizing or combusting a fuel to produce a feed stream for combustion in the turbine. Some catalytic combustors are also known for use in fuel processing applications such as those that convert hydrocarbon-based fuels to a hydrogen-rich reformate. By way of example, in a conventional steam reforming process, a hydrocarbon feed such as methane, natural gas, propane, gasoline, naphtha, or diesel, is vaporized, mixed with steam, and passed over a steam reforming catalyst. In such an application, process heat can be provided by a catalytic combustor for vaporizing and preheating the fuel and for steam generation. Process heat can also be used to heat one or more components of the fuel processor to an appropriate reaction temperature and to eliminate by-products produced by the fuel processor and/or a fuel cell stack integrated with the combustor.
Disadvantages of conventional catalytic combustors and the methods associated with them include delays and difficulties that are commonly encountered during start-up, difficulties in achieving complete combustion and difficulties in achieving and maintaining stable combustion temperatures at higher space velocities.